Biopsy forceps are commonly used during endoscopic procedures for removing tissue samples for pathological examination or for therapeutic purposes. For effective sampling it is important that a maximum force be transmitted from the handle of the endoscopic instrument to the end effector. Large clamping forces are often difficult to achieve due to the size restrictions of the end effector. Typically the arm of the lever, the dimensions or distances between the jaws or procedural member's pivot axis and the actuating hole are relatively short, which therefore limits the mechanical leverage of the end effector. It is especially evident when the procedural members are in a closed or nearly closed position. The procedural members therefore have small clamping forces resulting in poor grasping and retention of the tissue sample.
An endoscopic end effector with increased clamping force may be achieved by the deflection of the actuation means over the deflection member in the vicinity of the actuating hole. Increased clamping force is most required when the end effector procedural members are in the closed or nearly closed position.
Deflection of the actuation means changes the distribution of the pulling force applied to the handle of the endoscopic tool by the operator and transmitted by the actuation means to the end effector mechanism. The distribution of the forces is such that the clamping force is higher versus a clamping force derived only from the lever arm between the pivot axis of the jaws and the actuating hole.
Typical endoscopic surgical tools comprise of the handle actuating the end effector and end effector with procedural members performing a function. A hollow shaft or member extends between the handle and the end effector. The hollow member houses the actuation means that convert the actuation of the handle into the actuation of the procedural members of the end effector. The end effector is attached to the distal end of the hollow member and the handle is attached to the proximal end of the conduit.
Typical endoscopic end effectors comprise of procedural members and a clevis encompassing the procedural members. Actuation means are rotatably connected to the arms of the procedural members through the actuating holes. Proximal ends of the actuation means are attached to the movable sliding element of the handle. Procedural members are connected together by a rivet passing through the pivot axis holes. Often a flat member is present between the procedural members. The flat member may have a hole that accepts the rivet and is axial or nearly axial with the pivot axis holes of the procedural members. In essence the procedural members and the flat member are sandwiched pivotally together by the encompassing rivet. Often the clevis is also incorporated into this sandwich.
Prior art end effectors have been devised to address the some of the noted problems. For example, U.S. Pat. No. 4,763,668 issued to Macek on Aug. 16, 1988 et al discloses a biopsy forceps jaw assembly utilizing a linkage mechanism for the actuation of the jaws. The linkage mechanism provides increased clamping force. However the assembly process of the jaws and the number of individual components makes the device expensive to manufacture.
U.S. Pat. No. 4,887,612 issued on Dec. 19, 1989 to Esser et al discloses a biopsy forceps jaws mechanism which utilizes a cam linkage to actuate the jaws. In the closed or nearly closed position of the jaws this design does not offer an increased clamping force. Furthermore, the components of the jaws require expensive machining process and are not ideally suited for mass production of the disposable biopsy forceps.
U.S. Pat. No. 5,133,727 issued on Jul. 28, 1992 to Bales et al teaches a simplified construction of the biopsy forceps jaws using two actuating wires for the actuation of the jaws. This construction is suitable for mass production and assembly of the disposable biopsy forceps. However the clamping force of the jaws is less than in the linkage design. This manifests itself specifically when the jaws are in the closed or almost closed position. As noted above the clamping force is determined by the lateral distance between the pivot axis of the jaws and the actuation holes and it is limited by the constraints of the size of the channel that the jaws have to pass through during a procedure.
Referring to FIGS. 5 to 7, Boston Scientific Corporation Radial Jaw® 3 and Radial Jaw® 4 both incorporate a twist in a proximal end of the flat needle in the construction of the jaws. This twist provides for a limited deflection of the actuating wires and increased clamping force of the closing jaws. The twist is located at a distance from the actuating holes of the jaws therefore limiting the deflection angle and the resulting mechanical advantage. Also the twisted wings at the proximal end of flat needle flex back when tensioned by the actuating wires, therefore reducing the deflection angle and reducing the increase of the clamping force of the device. Furthermore, the stainless steel actuating wires rub against stainless steel twist which creates rough feel during the actuation of the jaws. Medical professionals prefer smooth opening and closing of the biopsy forceps.
U.S. Pat. No. 6,273,860 issued Aug. 14, 2001 to Kostylev et al discloses a design of the jaws assembly providing an increased clamping force of the biopsy forceps, especially as the jaws approach the closed position. The proposed design involves grooves around the back of the jaws and control wires sliding within these grooves. The construction of jaws proposed by Kostylev is expensive to manufacture and therefore not suitable for the mass production of the disposable biopsy forceps.
U.S. Pat. No. 7,105,000 issued Sep. 12, 2006 to McBrayer teaches us that the higher clamping force can be obtained by incorporating a circumferential ridge on the clevis. This ridge allows for an increased spacing between the pivot axis of the jaws and the actuating holes and therefore an increased clamping force of the closing jaws. The ridge however increases the diameter of the clevis. The diameter of the clevis is limited by the diameter of the channel in the endoscope through which the devices has to be pushed. Consequently, the increased clamping force is also limited by the diameter of the channel of the endoscope.
U.S. Pat. No. 7,223,272 issued May 29, 2007 to Francese et al proposes mounting of the jaws on non-collinear axes. This allows for increased spacing between the pivot axis of the jaws and the actuating holes, without an increase of the diameter of the clevis, and consequently an increased clamping forceps of the closing jaws. This design is however more complicated versus a design having just one pivot axis and therefore more expensive to manufacture.
Thus an end effector for a surgical instrument which has improved clamping force, easily fits within the diameter of the channel of the endoscope, is suited for mass production, is economical to machine process, allows for smooth operation, is disposable, and has an efficient and effective design is desirable.